💿🐜 Antkeeper source code
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144 lines
3.9 KiB
144 lines
3.9 KiB
/*
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* Copyright (C) 2023 Christopher J. Howard
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*
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* This file is part of Antkeeper source code.
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*
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* Antkeeper source code is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Antkeeper source code is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Antkeeper source code. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef ANTKEEPER_COLOR_XYZ_HPP
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#define ANTKEEPER_COLOR_XYZ_HPP
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#include <engine/math/vector.hpp>
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namespace color {
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/// @name CIE XYZ color space
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/// @{
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/**
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* Returns the luminance of a CIE XYZ color.
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*
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* @param x CIE XYZ color.
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* @return return Luminance of @p x.
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*/
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template <class T>
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[[nodiscard]] inline constexpr T xyz_to_luminance(const math::vec3<T>& x) noexcept
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{
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return x[1];
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}
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/**
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* Transforms a CIE XYZ color into the CIE xyY color space.
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*
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* @param x CIE XYZ color.
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* @return CIE xyY color.
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*/
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template <class T>
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[[nodiscard]] constexpr math::vec3<T> xyz_to_xyy(const math::vec3<T>& x) noexcept
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{
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const T sum = x[0] + x[1] + x[2];
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return math::vec3<T>{x[0] / sum, x[1] / sum, x[1]};
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}
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/**
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* CIE 1931 standard observer color matching function for the X tristimulus value.
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*
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* @param lambda Wavelength of light, in nanometers.
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* @return Matching X tristimulus value.
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*
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* @see match(T)
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*/
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template <class T>
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[[nodiscard]] T xyz_match_x(T lambda)
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{
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const T t0 = (lambda - T{442.0}) * ((lambda < T{442.0}) ? T{0.0624} : T{0.0374});
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const T t1 = (lambda - T{599.8}) * ((lambda < T{599.8}) ? T{0.0264} : T{0.0323});
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const T t2 = (lambda - T{501.1}) * ((lambda < T{501.1}) ? T{0.0490} : T{0.0382});
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const T x0 = T{ 0.362} * std::exp(T{-0.5} * t0 * t0);
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const T x1 = T{ 1.056} * std::exp(T{-0.5} * t1 * t1);
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const T x2 = T{-0.065} * std::exp(T{-0.5} * t2 * t2);
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return x0 + x1 + x2;
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}
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/**
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* CIE 1931 standard observer color matching function for the Y tristimulus value.
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*
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* @param lambda Wavelength of light, in nanometers.
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* @return Matching Y tristimulus value.
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*
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* @see match(T)
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*/
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template <class T>
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[[nodiscard]] T xyz_match_y(T lambda)
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{
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const T t0 = (lambda - T{568.8}) * ((lambda < T{568.8}) ? T{0.0213} : T{0.0247});
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const T t1 = (lambda - T{530.9}) * ((lambda < T{530.9}) ? T{0.0613} : T{0.0322});
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const T y0 = T{0.821} * std::exp(T{-0.5} * t0 * t0);
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const T y1 = T{0.286} * std::exp(T{-0.5} * t1 * t1);
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return y0 + y1;
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}
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/**
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* CIE 1931 standard observer color matching function for the Z tristimulus value.
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*
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* @param lambda Wavelength of light, in nanometers.
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* @return Matching Z tristimulus value.
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*
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* @see match(T)
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*/
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template <class T>
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[[nodiscard]] T xyz_match_z(T lambda)
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{
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const T t0 = (lambda - T{437.0}) * ((lambda < T{437.0}) ? T{0.0845} : T{0.0278});
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const T t1 = (lambda - T{459.0}) * ((lambda < T{459.0}) ? T{0.0385} : T{0.0725});
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const T z0 = T{1.217} * std::exp(T{-0.5} * t0 * t0);
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const T z1 = T{0.681} * std::exp(T{-0.5} * t1 * t1);
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return z0 + z1;
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}
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/**
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* Fitted piecewise gaussian approximation to the CIE 1931 standard observer color matching function.
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*
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* @param lambda Wavelength of light, in nanometers.
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* @return Matching CIE XYZ color.
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*
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* @see match_x(T)
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* @see match_y(T)
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* @see match_z(T)
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*
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* @see Wyman, C., Sloan, P.J., & Shirley, P. (2013). Simple Analytic Approximations to the CIE XYZ Color Matching Functions.
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*/
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template <class T>
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[[nodiscard]] math::vec3<T> xyz_match(T lambda)
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{
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return math::vec3<T>
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{
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xyz_match_x<T>(lambda),
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xyz_match_y<T>(lambda),
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xyz_match_z<T>(lambda)
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};
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}
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/// @}
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} // namespace color
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#endif // ANTKEEPER_COLOR_XYZ_HPP
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